1. Field of the Invention
This invention relates generally to telecommunications, and more particularly, to wireless communications.
2. Description of the Related Art
In a telecommunication system, a large geographically distributed network coverage area is typically partitioned into a multiplicity of mobile communication regions, such as cells, where each cell includes a communication node, such as a base station to realize wireless communications with one or more mobile stations or wireless devices within that cell. The network coverage area is commonly based on wireless links that are designed to operate at a minimum level consistent with Quality of Service (QoS) in an area where the mobile station has sufficient power to achieve a target signal-to-noise (SNR) ratio at a cell site that includes the base station.
Continued growth in the number of users of mobile communications means that many wireless network operators or service providers must find new ways of increasing the capacity of their networks. Antenna systems represent an area that may be developed to increase capacity in mobile communication networks. Specifically, many traditional installations of mobile communication base-station antennas make use of space-diversity techniques (e.g., Multiple Input Multiple Output (MIMO) systems), which require at least two antennas pointing in the same direction and separated from each other. A typical base station may now employ as many as six transmitting and six receiving antennas, each requiring its own duplex filter.
The main task of the duplex filter is to separate transmit and receive frequencies at the antenna port. A typical duplex filter thus has three ports, one for the antenna, one for the transmitter and one for the receiver. A typical duplex filter is composed of coaxial resonators that require advanced fabrication techniques and materials to achieve high Q-factors (e.g., ˜5000) that are needed to provide high filter selectivity. Filter selectivity is critical in a base station because very sensitive receivers are operated in parallel with strong transmitters. In some applications, MIMO systems have proven to be cost prohibitive because of the cost of the duplex filters alone.